1. Field of the Invention
This invention relates to liquid crystal colour displays in which information is displayed in one colour on a background of another colour.
2. Discussion of Prior Art
One known form of colour display uses a smectic liquid crystal material addressed by a laser in projection displays and digital storage devices; see for example F. J. Kahn, Applied Physics Letters, 22, p. 111 (1973); A. G. Dewey, Optical Engineering, Vol. 23, No. 3, p. 230 (1984); and H. Birecki et al, SPIE Proceedings Vol. 420 edited by A. E. Bell and A. A. Jamberdino (1983).
A typical projection display with smectic liquid crystal materials uses a scattering and a transmissive state of the smectic material to provide a display. Both the light scattering and transmissive states can be stable and co-exist in different parts of a display at the same time. Information is written as areas of light scattering texture on a background of light transmissive texture i.e. dark features on a light background; or visa versa. The display is monochrome. Multi-colour may be provided by using a plurality of systems, each with an associated filter, and combining the outputs say on a screen. This is quite complicated and expensive. The displays need a small highly localised light source, e.g. an arc lamp, and Schlieren stop optics. These are wasteful of power and make it difficult to obtain adequate display brightness.